The present invention relates to a lubricant sealed bearing for reciprocatively rotating members, of oil-less type reciprocating machines. Such machines include, for example, compressors, vacuum pumps, etc.
FIG. 1 shows a longitudinal sectional view of an oil-less type reciprocating motion compressor, as one example of oil-less type reciprocating machines, which compressor is applied to a grease sealed bearing. This bearing is one example of a conventional lubricant sealed bearings. FIG. 2 shows an enlarged longitudinal sectional view of a connecting portion of the compressor shown in FIG. 1, in which a small end part of a connecting rod and a piston pin are connected to each other. The oil-less type reciprocating motion compressor shown in FIG. 1 and FIG. 2 has an approximately cylindrical shaped cylinder 1, and a cylinder head 2 mounted on the cylinder 1 through a valve plate 3. A suction chamber 2A and a discharge chamber 2B are formed on the valve plate 3 located in this cylinder head 2. Also an approximately cylindrical shaped piston 4 is inserted to fit inside the cylinder 1. This piston 4 is reciprocatively movable in the up and down directions as viewed in FIG. 1 inside the cylinder 1. A compression chamber 5 as a sealing chamber is formed between the piston 4 and valve plate 3.
A suction hole 3A and discharge hole 3B are formed on the above mentioned valve plate 3. The suction chamber 2A and the discharge chamber 2B open into the compression chamber 5 through the suction chamber 3A and discharge chamber 3B, respectively. Also a suction valve 6 is provided on the compression chamber 5 side of the suction hole 3A. A discharge valve 7 is provided on the discharge chamber 2b side of the discharge hole 3B. Further one pair of through holes 4A, 4A are formed on left and right sides of FIG. 1 in a radial direction of the piston 4. An approximately cylindrical shaped piston pin 8 is inserted to be fitted inside the through holes 4A, 4A by means of pipe-shaped thermal insulating elements 9, 9 made of polytetrafluoroethylene etc.
A small end part 10A, which is a top end part of a connecting rod 10 viewed in FIG. 1, is connected to the center portion of the piston pin 8 and a bottom end (not shown) of this connecting rod 10 is connected to a crankshaft (not shown) so as to be rotationally movable to each other. Thus the connecting rod 10 connects the piston pin 8 and the above mentioned crankshaft to each other. Also, a bearing hole 10B, in which the piston pin 8 is inserted, is formed on the small end part 10A of the connecting rod 10. Thus the connecting rod 10 is connected with the piston 4 so as to be rotationally movable to each other by means of the piston pin 8 inserted in the bearing hole 10B of the small end part 10A.
A grease sealed bearing 11 is fitted as shown in FIG. 2 between an inner peripheral surface of the bearing hole 10B of the small end part 10A of the connecting rod 10 and a peripheral surface of the piston pin 8. This grease sealed bearing 11 has a plurality of needle rollers 12, 12, . . . as rolling elements each having an approximately cylindrical shape, a center lines of which plurality of rollers are parallel to a center line A of the piston pin 8. These needle rollers 12, 12, . . . are located at equal intervals from each other so as to surround a peripheral surface of the piston pin 8. Maintenance elements (not shown) for maintaining the needle rollers 12, 12, . . . at equal intervals from each other are located respectively on the intervals between the needle rollers 12, 12, . . . . Also, each of the needle rollers 12, 12, . . . rolls accompanying a rolling of the small end part 10A of the connecting rod 10 against the piston pin 8. The rolling course of the each of the needle rollers 12, 12, . . . describes a circle, a center of which circle coincides with the center line A of the piston pin 8. A smooth rotation of the small end part 10A of the connecting rod 10 against the piston pin 8 is ensured by these respective rolling movements of the needle rollers 12, 12, . . . between the small end part 10A and piston pin 8.
Further, holding rings 13, 13 are provided inside the bearing hole 10B of the small end part 10A so as to sandwich each of the needle rollers 12, 12, . . . by both end sides of an axial direction of the rollers 12, 12, . . . . These holding rings 13, 13 prevent the positions of the needle rollers 12, 12, . . . from shifting toward both side of the axial direction of the rollers 12, 12, . . . . Also approximately ring-shaped oil seals 14, 14 are provided on both sides of axial direction of the bearing hole 10B.
Further, in the grease sealed bearing 11, grease G for lubrication is filled in a space formed between the inner peripheral surface of the bearing hole 10B and the peripheral surface of the piston pin 8 and in the intervals between the needle rollers 12, 12, . . . . The grease G is sealed inside the grease sealed bearing 11 by the oil seals 14, 14.
In a conventional oil-less type reciprocating motion compressor having the above mentioned construction, the crankshaft is rotationally driven by an external driving source, and the connecting rod 10 connected to the crankshaft is reciprocatively moved. Also the connecting rod 10 is swung, being caused by the rotational motion of the crankshaft. This movement of the connecting rod 10 is transmitted to the piston 4 via the piston pin 8 and the grease sealed bearing 11, so that the piston 4 reciprocatively moves in the up and down directions as viewed in FIG. 1 inside the cylinder 1. During this reciprocating movement of the piston 4, the piston 4 is moved from a top dead point of the crankshaft to a bottom dead point of it, which movement is referred to as suction process. On the suction process, the pressure of the compression chamber 5 is reduced. Therefore the suction valve 6 is opened, and air is drawn into the compression chamber 5 from the suction chamber 2A through the suction hole 3A. Also air is drawn from outside to the suction chamber 2A. Further, a movement of the piston 4 from the bottom dead point of the crankshaft to the top dead point of it is referred to as a compression process. During the compression process, the air of the compression chamber 5 is compressed. Therefore the discharge valve 7 is opened, and the compressed air in the compression chamber 5 is discharged to the discharge chamber 2B through the discharge hole 3B. Then the compressed air discharged to the discharged chamber 2B is supplied to the outside.
According to one example of the conventional oil-less type reciprocating motion compressor described above, the grease sealed bearing 11 is provided between the piston pin 8 of the piston 4 and the small end part 10A of the connecting rod 10. Also each of the needle rollers 12, 12, . . . of the grease sealed bearing 11, the above mentioned piston pin 8 and the bearing hole of the small end part 10A are lubricated by the grease G. Each of the needle rollers 12, 12, . . . rotates along a circumferential direction on the peripheral surface of the piston pin 8, the rotation of the rollers 12, 12, . . . being caused by the rotation of the small end part 10A against the piston pin 8. There is a case where the grease G, which is filled in the equal intervals between the needle rollers 12, 12, . . . , is extruded to both sides in the axial direction of the rollers 12, 12, . . . , the extrusion being caused by the rotation of the each of the needle rollers 12, 12, . . . .
Each of the needle rollers 12, 12, . . . moves alternately in forward and reverse directions, resulting from the alternating rotation in both forward and reverse directions of the small end part 10A, this special movement being caused by the above mentioned swinging motion of the connecting rod 10. The swinging motion occurs when the connecting rod 10 is driven by the crankshaft. The rotation of each of the needle rollers 12, 12, . . . makes the grease G filling the intervals of between the needle rollers 12, 12, . . . shake violently. Also the grease G has a certain amount of inertia, because it has rather higher viscosity than other lubricants. Therefore there are some cases where the grease G cannot follow the alternate rotation of the needle rollers 12, 12, . . . . Due to this reason, in the case where the grease G is extruded to both end sides of the axial direction of each of the needle rollers 12, 12, . . . , this extruded grease G exerts a pressure against each of the oil seals 14, 14 of both end sides in the axial direction of the bearing hole 10B.
There is the case when the grease G, which is sealed inside the grease sealed bearing 11 by the oil seals 14, 14 as mentioned above, leaks outside the both end sides in the axial direction of each of the oil seals 14, 14. This leaking is caused from such portions of the seals 14, 14 that the sealing performance is weakened. Being weakened of the sealing performance there results in the above mentioned pressure of the grease G against the each oil ssal 14 being exerted by the alternating rotation of each of the needle rollers 12, 12, . . . . In that case, the quantity of the grease in the grease sealed bearing 11 decreases. Because of this, the quantity of the grease G in the periphery of each of the needle rollers 12, 12, . . . becomes short. Also the quantity of the lubrication in the periphery of each of the needle rollers 12, 12, . . . and between the piston pin 8 and the small end part 10A becomes insufficient. Therefore life time of the grease sealed bearing 11 is shortened. Also, there is a problem in that a part of the grease G, which leaks outside via each of the oil seals 14, 14, enters into the compression chamber 5. For example, this intruded grease is mixed with the compressed air in the compression chamber 5. As the result of this, clean compressed air cannot be supplied to the outside.